Patent GB-1209008-A (GB)
Title: Improvements in or relating to numerical control systems
IPC: G05B19/40
Filed: 1969-05-16
Abstract: 1,209,008. Control of stepping motors. FUJITSU Ltd. 16 May, 1969 [16 May, 1968], No. 25219/69. Heading H2J. In order to respond correctly to high-frequeny command pulses a stepping motor is connected to a smoothing circuit comprising a reversible counter in which the command pulses are stored. An oscillator generates pulses at a frequency proportional to the content of the counter, an " and " gate transmitting the output pulses from the oscillator to the motor when the stored number is not at zero. The output pulses are also fed back to the counter and tend to return the stored number to zero. The motor has five stator assemblies each having an exciting coil and sixteen projections, the rotor having the same number of projections. Stepping is effected by energizing a group of three coils and then a pair in sequence, the motor being reversed by changing the polarity of the command pulses. In a numerical control system, a smoothing circuit SCX receives pulses along channels TXP, TXN, so that motor PMX drives a machine along an X-axis in either direction. Smoothing circuit SCY is similarly energized through channels TYP, TYN, for reversible movement along a Y-axis. A selector MIX is connected to adding or subtracting terminals 82, 83, of a reversible counter RC, and determines the destniation of pulses from " and " gate AG1. Overlapping between command pulses from terminals 80, 81, and feedback pulses from the gate AG1 is prevented. A digital-to-analogue converter DAC is connected between counter RC and oscillator VO. The counter RC comprises flip-flops F0-F9, the content of the counter being detected by gates OR1-OR7. The output pulses from oscillator VO are applied to inverter 141 and flip-flops F10, F11, whereby the pulses at terminal 142 have a predetermined duration. Pulseshaping is effected by multivibrators OM1, OM2. The digital-to-analogue converter comprises a number of transistors whose bases are connected through resistors to terminals T16-T25. The content of the counter determines the number of transistors which are made conductive to select a number of resistors forming a bank connected to the oscillator, Fig. 14 (not shown). The oscillator comprises an emitter follower associated with a further pulsing trans istor having the respective primary and secondary windings of a transformer in its collector and base circuits. The " on " period of the further transistor is determined by the discharge of a capacitor, the output of the oscillator being taken from a further transformer winding, Fig. 15 (not shown). In another embodiment, a register, in which digital information is stored, is connected to a converter whose resistance is equivalent to the stored number. The converter is connected to a unijunction transistor oscillator providing pulses to the motor through a wave shaper, Fig. 19 (not shown). In a further arrangement, a digital-capacitor converter is connected between the register and the oscillator. A plurality of lines from the register, each representing a digit, are connected to the bases of a bank of transistors for determining the number of capacitors in circuit and the period of oscillation of the oscillator. The motor may take the form of a digital electro-hydraulic servo motor having a detector for generating signals in response to angular movement of the motor. The signals are applied to a valve whereby the movement of the motor corresponds to the number of command pulses.